Transistorized control circuit for magneto motor ignition systems

ABSTRACT

An additional winding is provided on the magneto of a magneto ignition system to provide base current, over a capacitor-diode network and a current limiting resistor, to the base of the ignition transistor to assure that the transistor will be switched and held conducting during positive half waves of the magneto output up to the moment of ignition, when a control circuit blocks the ignition transistor. The control winding may be on a magneto armature that serves both to feed the ignition control circuit and to operate as a spark coil, or it may be on an entirely separate armature, or on the lighting system armature of the magneto. Instead of such a control winding, a transformer may be provided in the primary circuit to develop the control voltage.

United States Patent Haubner et a1. Feb. 4, 1975 [541 TRANSISTORIZED CONTROL CIRCUIT 3,496,920 2/1970 Shano et a1. 310/70 R X O MAGNETO MOTOR IGNITION 3,500,809 3/1970 Hohne et a1. 315/218 SYSTEMS 3,504,373 3/1970 Strelow 315/218 3,630,185 12/1971 Struber et a1. 123/148 CD [75] Inventors: Georg Haubner, Berg; Walter Hofer, 3,732,483 5/1973 Katsumata 310/70 X Schwabach; Peter schmaldienst, 3,765,390 10/1973 Loudon et :11. 123/148 E Nurnberg, all of Germany P E J D M" rzmary xammer- 1 er [73] Assignee. Robert Bosch GmbH, Stuttgart, Assistant Examiner Roben J. Hickey Germany Attorney, Agent, or FirmFlynn & Frishauf [22] Filed: July 31, 1973 1 B R CT [57 A ST A [21] Appl' 384380 An additional winding is provided on the magneto of a magneto ignition system to provide base current, over [30] Foreign Application Priority Data a capacitor-diode network and a current limiting resis- Aug. 29, 1972 Germany 2242326 wr, o the e o the ignit transistor to assure that the transistor will be switched and held conducting [52] U.S. Cl. 322/17, 123/148 E, 310/70 A, during positive half waves of the magneto output up to 315/209 T, 315/218 the moment of ignition, when a control circuit blocks [51] Int. Cl. F02p 1/00, F02p 1/08, F02p 9/00 the ignition transistor. The control winding may be on [58] Field of Search 310/70 R, 70 A; 322/17, a magneto armature that serves both to feed the igni- 322/91, 94; 315/209, 218, 209 T; 123/148 15,, tion control circuit and to operate as a spark coil, or it 148 C1) may be on an entirely separate armature, or on the lighting system armature of the magneto. Instead of [56] Referenc Cit d such a control winding, a transformer may be pro- UNITED STATES PATENTS vided in the primary circuit to develop the control 3,398,353 8/1968 Noddin etal. 322/91 x voltage 3,484,677 12/1969 Piteo 310/70 R X 6 Claims, 4 Drawing Figures TRANSISTORIZED CONTROL CIRCUIT FOR MAGNETO MOTOR IGNITION SYSTEMS- Cross-reference is made to the following related applications of the same inventors:

Ser. No. 384,282, filed July 31, 1973 and Ser. No. 384,381, filed July 3l, 1973.

This invention relates to a control circuit for a magneto type ignition system of an internal combustion engine, using a controllable semiconductor device to interrupt the primary circuit of an ignition coil.

In so-called ignition coil systems a previously closed primary circuit of the ignition system is opened at the proper moment in the engine cycle, preferably by a power transistor. The magnetic field built up in the ignition coil by the primary current then collapses and induces a high voltage pulse in the secondary winding, which produces a spark at the spark plug gap.

If more sparks are to be produced, the primary circuit must first be closed again. In battery-powered ignition systems, the control voltage necessary to switch on the transistor can be obtained from the battery terminals. In so-lcalled magneto ignition systems, however, the magneto generator voltage that appears at the terminals of the armature is too small, when the primary circuit is short-circuited, to hold the transistor fully in its conducting condition. A fully conducting condition of the transistor is, however, necessary for building up a strong magnetic field in the ignition coil or in the magneto armature (which may be provided with two windings and function also as an ignition coil).

In a known form of transistorized magneto ignition systems, the ignition transistor is connected in the primary circuit in series with a resistor. When a positive voltage half wave appears in the magneto output, the ignition transistor is then switched on and maintained conducting until the moment of ignition as the result of the voltage drop that arises across this resistor. At the moment of ignition the base-emitter path of the ignition transistor is bridged by a short circuit, which removes the base current and thereby switches the ignition transistor into its blocking state. These and similar solutions of the problem have the disadvantage that the resistor loads down the primary circuit undesirably, particularly at high speeds, because it has a current limiting effect and therefore limits the build-up of the magnetic field in the magneto armature during positive voltage half waves. Hence, when the primary circuit is interrupted by switching of the transistor, the high voltage set up in the secondary winding of the armature on account of the starting and idleing speeds, the resistor must not be made too small, lest a sufficient control voltage should fail to be available for the ignition transistor at these low speeds.

In an improved known form of transistorized magneto ignition system, a separate winding. on the magneto generator provides base current to the ignition transistor through a current limiting resistor until the.

moment the ignition transistor is put into its nonconducting condition. Whereas this produces some improvement, there is still some loading of'the positive voltage half wave by this arrangement, which it would be desirable to avoid.

It is an object of the invention to provide a transistorized magneto ignition system in such a way that the magnitude of the primary current that is to be interrupted at the moment of ignition is substantially unaffected by the components in the primary circuit serving to control the semiconductor switching device. It is a further object of the invention to utilize some energy drawn from the preceding negative half wave of the magneto generator output to contribute to maintain the base current of the ignition transistor during the succeeding positive half wave, thus minimizing the loading of the latter.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the control electrode of the controlled semiconductor device in the primary circuit is connected over a series combination of a capacitor and a resistor to one end of a control winding on the spark coil or magneto armature of which the other end is connected to the primary circuit, and a diode is provided with its cathode connected to the junction of the capacitor and the resistor and its anode connected to the side of the circuit provided to the engine casing. The induced voltages in the armature winding supplying current to the switching path of the controlled semiconductor device and in the control winding above mentioned are substantially in phase. As already indicated, a power transistor is preferably used as the semiconductor device.

Voltage from the control winding is advantageously applied over a series capacitor, at least one diode and a resistor to the control electrode of the controlled semiconductor device. Another diode, oppositely poled, is preferably connected in series between the resistor and the control electrode of the semiconductor device. It is convenient to ground one side of the control winding, as well as one side of the armature winding, tothe vehicle chassis or engine casing to provide a so-called ground return for the circuits. Instead of the arrangement with one side of the control winding grounded, however, the control winding may be providedwith one end connected to the ungrounded end of the armature winding that supplies the primary circuit, and the other end connected tothe control terminal of the controllable semiconductor device over a coupling resistor. In this latter case the control winding may be wound on the same armature core as the armature winding, or it may be wound on a supplementary armature. The control winding may even be provided on a different armature used to supply lighting current.

The invention will now be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram of a magneto ignition system in which the base of the ignition transistor is connected to a control winding on the magneto armature;

FIG. 2 is an axial simplified view of a magneto generator in which a control winding is provided on a supplementary armature;

FIG. 3 is a diagram of an ignition system in which the control winding is provided on a supplementary armature, and

FIG. 4 is a diagram of an ignition system in which the control winding is part of a transformer provided in the primary circuit.

The ignition system shown diagrammatically in FIG. 1 is the ignition system of a one-cylinder gasoline engine, which is provided with a magneto generator 10 having an ignition armature I] wound to serve as an ignition coil. Its iron core 12 has two windings, the primary winding 12a and the secondary winding 12b. The armature I1 is affixed to the casing (not shown) of the gasoline engine and functions in cooperation with a V rotor 13 equippedwith permanent magnets 14. The rotor 13 is driven in the direction shown by an arrow by the crankshaft of the engine.

Whereas the secondary winding 12b is connected over an ignition cable 15 with a spark plug 16, the pri' mary winding 12a of the armature 11 is connected in a circuit, which may be called the primary circuit, in which is also found the collector-emitter path ofa semiconductor device, which in this case is the NPN ignition transistor 17. The emitter electrode of the transistor 17, like one side of the primary winding 12a, is grounded to the engine casing or vehicle chassis. The other end of the primary winding 12a is connected to the collector of the ignition transistor 17. A resistor 19 in series with a diode 18 bridges the primary winding for'the purpose ofloading the armature 11 during negative voltage half waves.

The base of the ignition transistor 17 is connected in a control circuit with a control transistor 20, the collector-emitter path of which is in parallel with the baseemitter path of the ignition transistor 17. The base emitter path of the control transistor 20 is connected across the output of a pulse transmitter 21, so that a pulse therefrom will trigger the ignition circuit. The pulse generator 21 has a pole piece 21a conductive to magnetic lines of force on the periphery of the rotor 13, which revolves in the direction shown by the arrow near the pole piece. The base of the control transistor 20 is also connected to the common connection of resistors 23 and 22, which bridge the primary winding 12a.

- The control winding 24 is provided on the iron core 12 of the ignition armature 11, with one end connected to the ungrounded end of the primary winding 12a and the other end connected over a current limiting resistor 25 to the base electrode of the ignition transistor 17.

The resistor 25 limits the current in the control circuit.

at high speeds. The primary winding 12a and the control winding 24 are wound in the same direction, so that the voltages induced in them are in phase.

In operation, either in starting or when the engine is running, the turning of the rotor 13 of the magneto 10 induces alternating currents in the windings of the armature 11. The negative voltage half waves of the primary winding 12a are loaded in the primary circuit by the resistor 19 acting over the diode 18 to the extent necessary to keep the high voltage induced in the secondary winding 12b from reaching a value sufficient to excite a spark in the spark plug 16. The ignition transistor 17-remains blocked, because its base likewise receives a negative potential over the resistor 25.

At the beginning of each positive voltage half wave produced in the primary winding 12a, the in-phase control voltage produced by the control winding 24 likewise goes positive. Base current then begins to be supconducting" condition. In consequence, the baseemitter path of the ignition transistor 17 is shortcircuited, and the previously flowing base current supplied over the resistor 25 is now diverted to the grounded side of the circuit over the switching path of the control transistor 20. The collector-emitter path of the ignition transistor 17 is immediately blocked by the switching off of the base current, thereby interrupting the primary circuit current. The magnettic field built up in the armature by the current now collapses, and a high voltage pulse is produced in the secondary winding 12b, as the result of which an ignition spark is pro duced at the gap of the spark plug 16.

Since at the same time a voltage is induced also in the primary winding 12a and in the control winding 24, it must be assured that the control transistor 20 will remain in its conducting condition even after the voltage pulse produced by the pulse transmitter 21 has fallen off. That is accomplished by the coupling resistor 23 which transmits the rise of the primary voltage to the base of the control transistor 20 and thereby holds the control transistor 20 in its conducting condition by a quick override, that in turn keeping the ignition transistor 17 blocked. Only by the end of the positive half wave of the primary voltage does the control transistor 20 go back to its nonconducting condition, for with the disappearance of the positive voltage supplied over the resistor 23, the base of the control transistor is brought to the same voltage as its emitter by the operation of the resistor 22. The succeeding negative half voltage wave produced in the primary winding 12a and in the control winding 24 is, as already explained above, of no effect on the ignition transistor 17. Only when the next positive voltage half wave arrives does the control winding 24 again switch the ignition transistor 17 into its conducting condition. The ignition cycle is repeated with each complete revolution of the pole piece 21a provided on the rotor 13 of the magneto 10.

The control winding of the ignition system can just as well be provided on a separate armature 30 spaced from the ignition armature 11. The supplementary armature 30 and the control winding 31 on it are shown in dashed lines in FIG. 1. One end of this control winding 31 is grounded to the chassis,-and the other is connected over the resistor 25 with the base electrode of the transistor 17. The positioning of the supplementary armature 30 and the direction in which the control winding 31 is wound are so to be chosen that the volt ages induced in the winding will be approximately in phase with those induced in the primary winding 12a. Such a supplementary armature 30 and its control winding 31 operate in the same manner as the control winding 24 and the ignition armature 11.

FIG. 2 shows in greatly simplified fashion the construction of a magneto generator 40, illustrating a kind of magneto generator that may be used for an ignition system conforming to FIG. 1. Its rotor 41, designed to revolve in the direction shown by the arrow, is fixed on the crankshaft (not visible in the drawing) of the engine and is provided with permanent magnets providing the poles 42 arranged in alternating polarity, symmetrically distributed on the inner circumference of the rotor. Inside the rotor 41 is a stationary armature plate 43 mounted on the motor casing. The armature plate 43 carries the ignition armature 44, a lighting system armature 45 and a supplementary armature 46, as well as a magnetic pulse transmitter 47. The ignition armature 44 and the lighting system armature 45 are located diammetrically opposite each other. The supplementary armature 46 is arranged between the pole pieces of the armatures 44 and 45 in such a way that the supplementary armature 46 has a shift of 90 with respect to the ignition armature 44. The supplementary armature 46 carries a control winding 48, wound in a direction such as to provide induced voltages in phase with the voltages induced in the ignition armature 44. The pulse transmitter 47 functions in cooperation with a magnetically soft pole piece (not shown in the drawing) that moves past the pole piece of the pulse transmitter 47, once for each full revolution of the rotor 41 and thus triggers a spark in the manner described in connection with FIG. 1.

FIG. 3 shows an ignition system for the engine of a motor vehicle corresponding in principle to the circuit construction of the ignition system of FIG. 1. The same components are accordingly identified with the same reference numerals. A difference from FIG. 1 in this case is the fact that the ignition armature 11a of the magneto a is built without a control winding. The control winding is in this case provided on the lighting system armature 50, which also functions in cooperation with the rotor 13. The lighting system armature winding 51 is connected over the light switch 52 to the lighting system 52a of the motor vehicle. The control winding 53 is arranged in series with the lighting system winding 51, and the free end of the latter is grounded to the engine casing or vehicle chassis.

Another difference between FIG. 3 and FIG. 1 and this time a distinguishing feature of the present invention, unlike the difference previously mentioned, is the provision of means for boosting the effect of the control winding by adding a voltage accumulated by charging a capacitor during the preceding negative halfwave of the magneto generator output.

The free end of the control winding 53 is connected over a capacitor 54, a current limiting resistor 55 and a diode 56 with the base electrode of the ignition transistor 17. A diode 58 is provided with its anode connected to the groundside of the circuit, and its cathode connected to the common connection of the capacitor 54 and the resistor 55. The ungrounded end of the primary winding 12a of the ignition armature 11a is, finally, connected over a current limiting resistor 57 to the base electrode of the ignition transistor 17.

By proper spacial arrangement of the two armatures.

11a and 50 of the magneto 10a and proper winding direction for-the control winding 53, it is possible to obtain the result that the voltage induced during operation of the engine in the control winding 53 and the lighting system winding 51 is approximately in pace with thee voltage of the primary winding 12a. As already explained in connection with FIG. 1, the ignition transistor 17 remains blocked during the progress of a negative voltage half wave produced by the primary winding 12a. The negative voltage half wave appearing at the same time in the control winding 53 and lighting system winding 51 charges the capacitor 54 over the diode 58. During the succeeding positive voltage half wave of the control winding 53, the positive voltage developed in the winding is put in series with the charged capacitor 54 and the combined voltage, applied over the resistor 55 and the diode 56, drives a base current which switches the ignition transistor 17 fully into its conducting state. At the same time a positive voltage half wave also arises in the primary winding 12a and drives a strong current in the primary circuit, which is now practically short-circuited. That current is interrupted at the moment of ignition, when a timing pulse produced by the pulse transmitter 21 switches the control transistor 20 to its conducting condition, thus short-circuiting the base-emitter path of the ignition transistor 17, immediately causing the latter to block. The strong magnetic field built up by the primary current in the ignition armature Ila now collapses, so that a high voltage pulse is induced in the secondary winding 12b of sufficient potential to produce an ignition spark in the spark plug I6. Since the capacitor 54 now discharges over the switching path of the control transistor 20, the capacitor 54 will be ready to be charged up again by the next negative voltage half wave produced by the control winding 53. The ignition cycle can be repeated with each full period of the voltages in the ignition and lighting system armatures, or with each full revolution of the rotor 13.

The control winding 53 is so arranged in circuit, that a failure of the capacitor 54 that short-circuits the capacitor can be tolerated. In that case the positive voltage half wave of the control winding 53 and of the lighting system winding 51, which are now the only voltages effective on the base of the ignition transistor 17, are sufficient to switch the ignition transistor 17 fully into its conducting condition.

In the case of failure of the control winding 53 for example, by short-circuiting of one or more turns the lighting system winding 51 may serve as a control winding. This is indicated by the dashed line connection 59 in FIG. 3. When this connection is made, however, the capacitor 54 must be operative, because the capacitor substantially increases the positive voltage effective at the base of the ignition transistor 17, an effect which is needed if only the winding 51, without the winding 53, is operative.

The ignition system shown in FIG. 3 is so arranged that even upon total failure of the lighting system armature 50, the gasoline engine will continue to run with reduced ignition voltage and slightly increased starting speed. In this case the necessary base current for switching the ignition transistor 17 flows over a second control path from the primary circuit, over the resistor 57, to the base of the ignition transistor 17. The diode 56 in this situation prevents the control current from leaking away through the lighting system.

FIG. 4 shows an embodiment of the invention that is further simplified, as compared with FIG. 3. In this case the control winding is provided by a transformer 60. The same components are here also identified by the same corresponding reference numerals. The transformer 60 has its primary winding 60a in the primary circuit of the ignition system, and its secondary winding 60b connected at one end to the primary circuit and at the other end over a current limiting resistor 61 -to the base of the ignition transistor 17. During operation of the motor, as already explained in connection with FIG. 1, the negative voltage half waves have no effect on the ignition transistor 17. When a positive voltage half wave begins, positive potential is provided over the secondary winding 60b of the transformer 60 and over the resistor 61 to the base of the previously blocked transistor 17. Because the emitter of this transistor is held to ground" potential, the collector-emitter path of the ignition transistor 17 is next made slightly conducting. The current in the primary circuit of the ignition system now begins to flow. This current builds up a magnetic field in the transformer, and the change in the magnetic field (dQ/dt) excites a voltage in the secondary winding 60b of the transformer 60. The transformer 60 is now so connected that the voltage induced in the secondary winding 60b, upon rise of the primary current, applies positive potential over the resistor 61 to the base of the ignition transistor l7 that is effective to increase the base current. and thereby to drive the transistor 17 farther into its conducting condition. The increase of the base current causes furtherincrease of the primary current, so that a positive feedback effect is provided between the primary current and the base current. The resistor 61 serves to limit the base current at high speeds.

A further advantage of this circuit is the effect of the secondary winding 60b upon interruption of the primary current at the time of ignition, which causes the immediate blocking of the ignition transistor 17 by the pulse transmitter 21 as explained in more detail in connection with FIG. 1. At this time the voltage produced in the secondary winding 60b of the transformer 60 is in opposition to the voltage peak produced in the primary circuit, and hence limits the control current diverted over the control transistor 20.

Although the invention has been described with respect to particular illustrated embodiments, variations and modifications are possible within the inventive concept which may involve circuit arrangements in which individual components are differently constituted. It is essential, however, that over the entire range of motor speeds the semiconductor device in the primary circuit must be switched fully into its conducting condition on the arrival of each voltage half wave of a particular polarity, positive in the examples here given, and hence the control voltage for the semiconductor device must be provided by a control winding on a scale that is sufficient for switching the semiconductor device, even at low speeds of the motor and hence of the rotor of the magneto 10.

In place of the ignition transistor 17, for example, the semiconductor device could also be provided in the form of a transistor pair or double-transistor in the well-known Darlington circuit. Likewise the control transistor can be replaced by a semicontrolled' recitifier (SCR), an SCR tetrode or a triac, in which case the coupling provided over the resistors 22 and 23 can if desired be dispensed with. Semiconductor controlledrectifiers are sometimes known as thyristors. Another possible modification is to provide an ignition coil separate from the ignition armature 11, with its own primary winding in the primary circuit. The control winding, furthermore, can be provided on an armature arranged along side or otherwise adjacent to the ignition armature or to the light system armature.

Whether the ignition coil providing a high voltage winding is built into the magneto generator or, as just mentioned above is separate, the high voltage winding constitutes in each case a voltage step-up means coupled with the magneto armature.

We claim:

1. In an internal combustion engine ignition system having a magneto generator with a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with said magneto armature, which means is coupled with a lowvoltage winding of said armature and connected by ignition cable to at least one spark plug, said ignitionsystem having also a spark-timing pulse generator operated in synchronism with said engine.

an ignition control circuit for connection to said lowvoltage winding of said armature, comprising:

a controllable semiconductor device (17) having its switching path in circuit with said low-voltage winding;

means to supply the output of said pulse generator (27) to the control electrode of said semiconductor device (17);

control winding means (24, 30, 53, b) for electromagnetically deriving from electrical power supplied by said magneto generator, a voltageto supply control path current to said semiconductor device (17) during those half cycles of the output of said magneto armature for which said semiconductor device (1 17) is poled favorably for conduction. said control winding means having one end connected to the circuit in which said low-voltage winding is connected and being subject to a changing magnetic flux during the rise of current in said circuit;

resistance means (15) and at least one capacitor (54) connected in series between the other end of said control winding means and said control electrode of said semiconductor device (17); and

a diode (58) having its anode connected! to the side of said circuit grounded to the casing of said engine and its cathode connected to the junction of said resistance means (55) and said capacitor (54).

2. An ignition control circuit as defined in claim 1, in which at least one diode (56) is connected in series with said resistance means (55) and said capacitor (54) between one end of said control winding means (53) and said control electrode of said semiconductor device (l7).

3. An ignition control circuit as defined in claim 1, in which said low-voltage .winding (12a) has one end grounded to the casing of said engine and the other end connected over resistance means (57) to the control electrode of saidsemiconductor device (17).

4. An ignition control circuit as defined in claim 1, in which said control winding means is a winding (53) provided on an armature (50) of said magneto generator separate from said magneto armature (11) and carrying a winding (51) for supplying lighting circuits.

5. An ignition control circuit as defined in claim 4, in which said winding constituting said control winding means (53) is connected in series with said winding (51) for supplying lighting circuits.

6. In an internal combustion engine ignition system having a magneto generator with a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and

having voltage step-up means coupled with a lowvoltage winding of said armature and connected by ignition cable to at least one spark plug, said ignition system having also a spark-timing pulse generator operated in synchronism with said engine,

an ignition control circuit for connection to said lowvoltage winding of said armature, comprising:

a controllable semiconductor device (17) having its.

switching path in circuit with said low-voltage winding;

means to supply the output of said pulse generator (27) to the control electrode of said semiconductor device (17); a transformer (60) having its primary winding (60a) in circuit with said low-voltage winding (12a) of said armature and said switching path of said controllable semiconductor device (17) and having its secondary winding (60b) for supplying control path current to said semi-conductor device (17) during those half cycles of the output of said magsaid low-voltage winding is connected.

* 1 t I. k 

1. In an internal combustion engine ignition system having a magneto generator with a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with said magneto armature, which means is coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, said ignition system having also a sparktiming pulse generator operated in synchronism with said engine, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a controllable semiconductor device (17) having its switching path in circuit with said low-voltage winding; means to supply the output of said pulse generator (27) to the control electrode of said semiconductor device (17); control winding means (24, 30, 53, 60b) for electromagnetically deriving from electrical power supplied by said magneto generator, a voltage to supply control path current to said semiconductor device (17) during those half cycles of the output of said magneto armature for which said semiconductor device (17) is poled favorably for conduction, said control winding means having one end connected to the circuit in which said low-voltage winding is connected and being subject to a changing magnetic flux during the rise of current in said circuit; resistance means (15) and at least one capacitor (54) connected in series between the other end of said control winding means and said control electrode of said semiconductor device (17); and a diode (58) having its anode connected to the side of said circuit grounded to the casing of said engine and its cathode connected to the junction of said resistance means (55) and said capacItor (54).
 2. An ignition control circuit as defined in claim 1, in which at least one diode (56) is connected in series with said resistance means (55) and said capacitor (54) between one end of said control winding means (53) and said control electrode of said semiconductor device (17).
 3. An ignition control circuit as defined in claim 1, in which said low-voltage winding (12a) has one end grounded to the casing of said engine and the other end connected over resistance means (57) to the control electrode of said semiconductor device (17).
 4. An ignition control circuit as defined in claim 1, in which said control winding means is a winding (53) provided on an armature (50) of said magneto generator separate from said magneto armature (11) and carrying a winding (51) for supplying lighting circuits.
 5. An ignition control circuit as defined in claim 4, in which said winding constituting said control winding means (53) is connected in series with said winding (51) for supplying lighting circuits.
 6. In an internal combustion engine ignition system having a magneto generator with a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, said ignition system having also a spark-timing pulse generator operated in synchronism with said engine, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a controllable semiconductor device (17) having its switching path in circuit with said low-voltage winding; means to supply the output of said pulse generator (27) to the control electrode of said semiconductor device (17); a transformer (60) having its primary winding (60a) in circuit with said low-voltage winding (12a) of said armature and said switching path of said controllable semiconductor device (17) and having its secondary winding (60b) for supplying control path current to said semi-conductor device (17) during those half cycles of the output of said magneto armature for which said semiconductor device (17) is poled favorably for conduction; and resistance means (61) connected in series between one end of said secondary winding (60b) and said control electrode of said semiconductor device (17), the other end of said secondary winding being connected to a point of said circuit in which said low-voltage winding is connected. 